Supernatural (Dipper x Reader x Bill)

When we were all yonger we had imaginary friends, a young girl named (y/n) had one, except, he was not so imaginary. He went by the name Bill. The two were inseparable, until, (y/n) made 2 friends. Their names were Dipper and Mabel Pines. Bill was soon forgotten and replaced by the Pines twins. The 3 of them were best of friends until (y/n) had to move. After receiving a gift from the Pines twins she leaves to live in ((s/t) state name). After 7 years she goes to Gravity Falls to study the supernatural and reunites with her child hood friends, but not before bumping into her not so imaginary friend, a yellow dream demon we all know and love.